Codan NGT AR, Руководство по началу работы

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HF radio transmission
NGT Transceiver Getting Started Guide 77
Frequency, distance and time of day
The extent to which an HF radio wave is reflected depends on
the frequency that is used. If the frequency is too low, the
signal is absorbed by the ionosphere. If the frequency is too
high, the signal passes straight through the ionosphere. Within
the HF band, low frequencies are generally considered to be in
the range of 2 to 10 MHz. High frequencies are above
10 MHz.
A frequency chosen for daytime transmission may not
necessarily be suitable for night-time use. During the day, the
layers of the ionosphere are thick. The layers absorb lower
frequencies and reflect higher frequencies. At night, the
ionosphere becomes very thin. The low frequencies that were
absorbed during the day are reflected, and the high frequencies
that were reflected during the day pass straight through.
Summer HF radio communications usually operate on higher
frequencies than those used in winter over the same distance.
Solar activity varies over an 11 year cycle. Higher frequencies
need to be used during periods of peak activity.
It is important to remember that you may need to change the
frequency you are using to achieve the best communication.
The general rules of thumb for HF radio communications are:
• the higher the sun, the higher the frequency
• the further the distance, the higher the frequency